People taking blood thinning medications should not use bromelain. Bromelain's anti-clotting activity in the blood means that it should not be combined with medications, such as warfarin (Coumadin), heparin, or aspirin that are used to prevent clotting or to thin the blood. It is also possible that bromelain could cause problems with bleeding if it is combined with other complementary therapies that thin the blood, such as garlic or gingko biloba.

As with any medicine or supplement, consult your physician before taking bromelain. If you are already taking bromelain, be sure to tell your physician before he or she writes a prescription for blood thinning agents.